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Interactive effects of vertical mixing, solar radiation and microbial activity on oceanic dimethylated sulfur cycling

AuthorsGalí, Martí
AdvisorSimó, Rafel
Issue Date23-Oct-2012
PublisherUniversidad Politécnica de Cataluña
CSIC - Instituto de Ciencias del Mar (ICM)
AbstractMicroscopic plankton thriving in the sunlit upper ocean play a key role in the biogeochemical functioning of the biosphere. The production and subsequent emission of volatile compounds is one of the numerous ways by which they participate in the cycling of elements and in uence the Earth's climate. Dimethylsulde (DMS), produced by enzymatic decomposition of the algal intracellular compound dimethylsulfoniopropionate (DMSP), is the more abundant organic volatile in the upper ocean. Its global emission amounts ca. 28 Tg S per year, and represents the main biogenic source of sulfur to the troposphere and about 30% of the total S emission (anthropogenic, biogenic and volcanic). Atmospheric oxidation of DMS contributes to atmospheric acidity, and is believed to promote the formation and growth of aerosols. Furthermore, DMS-derived sulfate aerosols have been suggested to cool the climate by reducing the amount of shortwave solar radiation reaching the Earth's surface by scattering solar radiation and, more important, by acting as cloud condensation nuclei. The `CLAW' hypothesis postulates that, if oceanic DMS emission was in turn stimulated by solar radiation, a regulatory feedback mechanism could operate between marine plankton and the radiative budget over the oceans. However, the relationship between DMS emission and solar radiation is not straightforward, since a number of biochemical and photochemical transformations come into action from the moment DMSP is synthesized by phytoplankton until DMS is emitted. These transformations are intimately linked to the physical environment, the ecological setting and the microbial interactions, rendering the picture of dimethylated sulfur cycling a lot more complicated. Surprisingly, though, the seasonal cycle of seawater DMS concentration seems to follow that of solar radiation in the majority of oceanic regions, regardless their productivity regimes. This characteristic feature of oceanic DMS, while broadly accepted, is not yet well understood. The premise of this thesis is that, to understand this emerging pattern, we need to understand what regulates the DMS production and consumption processes and their balance (that is, DMS budgets). To this end, we have studied the response of biotic and abiotic DMS cycling to solar radiation by means of incubation experiments. At another level, we have studied the response of ecosystem DMS budgets to dierent radiation climates, and from polar to subtropical areas. Since the depth of the upper mixed layer regulates the amount and spectral composition of the `light' seen by the cells and molecules, our studies have been backed by a careful characterization of underwater radiation elds and vertical mixing dynamics
DescriptionMemoria de tesis doctoral presentada por Martí Galí Tàpias para optar al grado de Doctor en Ciencias del Mar en el Departament d'Enginyeria Hidràulica, Marítima i Ambiental de la Universitat Politécnica de Catalunya (UPC), realizada bajo la dirección del Dr. Rafel Simó Martorell del Departament d'Enginyeria Hidràulica, Marítima i Ambiental de la Universitat Politècnica de Catalunya (UPC) y del Institut de Ciències del Mar (ICM-CSIC),-- 214 pages
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